Michael S. Lewis-Beck, editor
Sage Publications, 1993
Buku Referensi
Thurtone, L.L., author
Macmillan, 1925
Buku Teks
Wallis, W. Allen, author
The Free Press, 1966
Buku Teks
Leonard, J Martin, author
Teach Yourself Books, 1974
Buku Teks
Bowley, Arthur, author
Staples Press, 1948
Buku Teks